Hubble Space TelescopeMorphologies of Local Lyman Break Galaxy Analogs. I. Evidence for Starbursts Triggered by Merging

Abstract

Heckman and coworkers used the GALEX UV imaging survey to show that there exists a rare population of nearby compact UV-luminous galaxies (UVLGs) that closely resemble high-redshift Lyman break galaxies (LBGs). We present HST images in the UV, optical, and H and resimulate them at the depth and resolution of the GOODS/UDF fields to show that the morphologies of UVLGs are also similar to those of LBGs. Our sample of eight LBG analogs thus provides detailed insight into the connection between star formation and LBG morphology. Faint tidal features or companions can be seen in all of the rest-frame optical images, suggesting that the starbursts are the result of a merger or interaction. The UV/optical light is dominated by unresolved ($100Y300 pc) super starburst regions (SSBs). A detailed comparison with the galaxies Haro 11 and VV 114 at z ¼ 0:02 indicates that the SSBs themselves consist of diffuse stars and (super) star clusters. The structural features revealed by the new HST images occur on very small physical scales and are thus not detectable in images of high-redshift LBGs, except in a few cases where they are magnified by gravitational lensing. We propose, therefore, that LBGs are mergers of gas-rich, relatively low-mass (M Ã $ 10 10 M ) systems, and that the mergers trigger the formation of SSBs. If galaxies at high redshifts are dominated by SSBs, then the faint-end slope of the luminosity function is predicted to have slope $ 2. Our results are the most direct confirmation to date of models that predict that the main mode of star formation in the early universe was highly collisional.

The environment of HII galaxies revisited

“…The biases introduced by multiplicity, rotation, and contamination by the underlying galaxy (e.g. Overzier et al 2008;Amorin et al 2012) are minimized by selecting only objects with emission lines of high equivalent width and line profiles that are well fitted by a single Gaussian.…”

Analyzing low signal-to-noise FUSE spectra

“…distribution (e.g. Overzier et al 2008). Haro 11 has a complex morphology with three main star-forming knots and seems to be dynamically unrelaxed, remniscent of a merger event (Östlin et al 2001).…”

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

“…Over the last decade, the advent of all-sky optical and UV surveys such as the Sloan Digital Sky Survey (SDSS; Abazajian et al 2003) and the Galaxy Evolution Explorer (GALEX; Martin et al 2005), along with other smaller surveys, have allowed us to systematically search and characterize relatively large samples of extreme emission-line galaxies (EELGs) out to the frontiers of the local Universe (z < ∼ 0.3, e.g., Kniazev et al 2004;Kakazu et al 2007;Overzier et al 2008;Salzer et al 2009;Cardamone et al 2009;Cowie et al 2010;Izotov et al 2011;Shim & Chary 2013). This has made it possible to discover an increasing number of extremely compact, low-metallicity galaxies with unusually high specific star formation rates (SFR, sSFR = SFR/M ∼ 1−100 Gyr −1 ), such as the green peas (Cardamone et al 2009;Amorín et al 2010) and a handful of extremely metal-poor galaxies (XMPs; Z < ∼ 0.1 Z Kunth & Östlin 2000) at 0.1 < ∼ z < ∼ 0.4 (e.g., Kakazu et al 2007;Hu et al 2009;Cowie et al 2010).…”